Student of Thales, and teacher to Anaximenes and Pythagoras (570 ~ 495 BC).

He believed the world was made of a mystical substance he called the boundless (in Greek, apeiron) or the limitless.

Since all other things (matter) decayed and whithered, the eternal substance which gave birth to this universe and many other universes could not be made of them. Instead, the "boundless" was the source of everything.

He discovered that rain water came from evaporation.

He introduced a Babylonian sundial with a gnomon (a device that measures time and other mathematical calculations) to the Greeks

Spent his life in markets and city squares, talking with people. He didn't lecture. He discussed.

Unlike his predecessors, he shifted focus away from nature and onto the human mind; the person and the society he lives in.

He believed that knowledge can only come from within. Can't be imposed from outside. He believed he gained wisdom from a divine inner voice.

He's famously said: "One thing only I know, and that is that I know nothing."

He believed that one who knows what good is, will do good. Meaning, those who do wrong do so because they don't know what is good. This is why it was important to learn more and seek truth. Doing the right thing brings us happiness.

He was accused of "introducing new gods" and "corrupting the youth," and sentenced to death by poison.

DemocritusΔημόκριτος

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460 BC.
Abdera, Thrace (Ancient Greece)
370 BC.
The Atomic Universe

Nothing really changes because everything was made of immutable and eternal atoms. The word "atom" in Greek means "un-cuttable."

He believed atoms come in different shapes and textures, with hooks and barbs, but that all were solid. Like lego blocks

When one dies, the atoms break apart and join again to form a new body

There was nothing other than atoms and void (no spirits or invisible forces the way we think of them). He believed souls were made of atoms too.

AntisthenesἈντισθένης

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445 BC.
Athens
365 BC.
Father of the Cynics (and student of Socrates)

He believed that virtue can be taught, that virtue is the the most noble characteristic, and that through virtue one can attain happiness.

He was the father of the Cynics, philosophers who believed that happiness cannot be gained from material things. He believed he learned this from Socrates, who once said after gazing at a store: "What many things I don't need!"

Happiness cannot be found in material things, and unlike material things, when happiness is attained, it can never be lost, because it is not material.

Shouldn't worry about pain and suffering falling upon you or others, but endure.

He believed that there is only one "natural" God, who is beyond human comprehension or representation.

Student of Socrates and founder of "the Academy," named after the groves where he built it: the Groves of Academus, where Academus was buried, and where Plato used to teach.

Theory of Ideas: behind all material things (which flow), there is an immutable and intangible form. He called these perfect eternal moulds that made everything we see as "ideas." So behind the horse, there is the idea of a horse.

Since the material world was in flow (it will eventually die or dissolve), our senses cannot be trusted to gain eternal knowledge. Our reason, however, was able to access the real world (the world of ideas) which is behind the material world; the world of the senses.

He believed the soul, which was "reason," was eternal because it could recognize the eternal and immutable things in the world of ideas. The soul exists before it enters the human body, and when it enters, it loses memory of everything in the world of ideas. But the world of the senses helps it remember.

The immortal soul yearns to return to the world of ideas, and be freed from the body.

He believed men and women had equal souls (equal intelligence).

Gave a full description of his vision of Utopia in The Republic (a dialogue between Socrates and others), in which a caste system is in place for the benefit of all, and that society must be led by a philosopher king.

DiogenesΔιογένης ὁ Σινωπεύς

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412 BC.
Sinope, Ionia
323 BC.
Living in a barrel

Alexander the Great is said to have asked Diogenes, while he was sitting down next to his barrel enjoying the sun light: "is there anything you want? I will make it come true." Diogenes replied: "Yes, move a step aside. You are blocking the sun."

Like Antisthenes, he believed that virtue is the greatest characteristic to achieve in life, and that it is virtue through action that counts.

He taught many great philosophers, including Zeno, who later became the founder of the Stoic philosophy.

When asked where he was from, he would say "I am a citizen of the world," in Greek: cosmopolitan.

He believed human beings lived artificially and hypocritically, and that they should learn life from a dog, which Diogenes believed to be more virtuous. The word "cynic" comes from the Greek word "dog-like."

Reversed Plato's "theory of ideas." Aristotle believed the "world of the senses" was the real world. The world of ideas was born out of our innate ability to reason and imagine, but only after we have perceived the real world with our senses.

Everything is made of "substance" and "form." But unlike Plato, it was the substance that was real. The form was only in our heads; the way we classify things into species.

Substance has potential to come in many (yet limited number of) forms. Change in nature occurs from the potential to the actual.

He believed that there are four types of causality for everything: material cause (causality as we know it today), efficient cause (things happen because it is the most efficient way for them to happen in that particular way), formal cause (something acts in a way because of its form), and final cause (the purpose of the thing that happens).

He founded Logic; syllogisms (e.g. if A = B and B = C, then A = C).

He differentiated between living and non-living things by stating that only living things have the potential to change from within.

He believed in God, the "first mover."

On happiness: Man can only find true happiness by achieving all three kinds of happiness: (1) pleasure and enjoyment, (2) living as a free and responsible citizen, and (3) living as a thinker and philosopher.

Ethics: A harmonious life can only be achieved through balance: not too much, not too little, but in between.

Women: are incomplete, because they are passive, whereas men are active. A man sows his seed (and in his seed is the complete form of the human being). A woman was the field which gave substance to the form provided by man.

When the torch of philosophy and science is passed to the Arabs and Persians, during the Islamic Golden Age (700 ~ 1250 AD), Aristotilian philosophy is revived and considered supreme, and Aristotle becomes known simply as The Philosopher.

EpicurusἘπίκουρος

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341 BC.
Athens
270 BC.
Father of Epicureanism

The purpose of philosophy is to attain happiness and tranquility (ataraxia).

He is the founder of the Epicurean school, known as "the Garden" because it was located in a garden. It was the first philosophy school to allow women

He believed that when pain is successfully avoided, we no longer need pleasure. The soul reaches ataraxia (tranquility).

Unlike the Stoics, he believed a happy life avoids getting involved in politics. He advocated a "life of obscurity."

There is no after life. When we die, both soul and body die.

He believed in gods, but that they don't involve themselves in human affairs (no reward or punishment). His proof was known later as the Epicurean Paradox: If God is willing to prevent evil but not able, then he's not omnipotent. If he's able but not willing, then he's malevolent. If he's both able and willing, then why is there evil? And if he's neither able nor willing, why call him God?

His philosophy led to medical therapies (physical and mental) and treatments that involved massages and diets.

ZenoΖήνων ὁ Κιτιεύς

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334 BC.
Citium, Cyprus
262 BC.
Student of Socrates and father of the Stoics.

God is the universe (the Logos). The primary substance is fire; an "artistic" fire, because creation is the work of art. He agreed with Heraclitus that the universe was in flow: goes through the cycle of creation and destruction (constant change).

Like Socrates, he believed in natural law (universal rightness that held true regardless of time and place). Stoics were political and concerned with social issues.

He believed in fate, and that the only way to achieve happiness (which was the aim of life) was when one's "reason" matches the universal reason "Logos."

Studied philosophy in Alexandria then moved to Rome, bringing with him a competitive theology to Christianity, which only ended up becoming part of Christian thought.

Darkness does not exist. It is merely the absence of light, the source of which is "the One," God. Everything is one; everything is God.

The immortal soul is illuminated by the light from the One. Matter is the darkness that has no real existence.

He believed that his soul experienced merging with God through mysticism.

Had a great influence on Islamic philosophy, that the Fatimid dynasty (909 ~ 1171 AD) based in Egypt adopted his views.

St. Augustine of Hippo (354 ~ 430 AD), who built upon Plotinus's philosophy, is recognized as an important philosopher in Europe who helped shape Christian theology and philosophy for centuries to come, until St. Thomas Aquinas (1225 ~ 1274 AD) showed up to the scene.